Installation Manual

Chapter 2 N38143
Page 6
Part wet/part dry systems
In some installations this arrangement may be chosen in place of a water lift. The part wet/part dry system
allows the engine exhaust manifold outlet to be near or below the waterline, and provides protection against
sea water back-ooding into the engine exhaust.
The general arrangement (D) shows that the dry part of the system extends to a safe height above the water
line, using an elbow (D1), a stainless steel bellows (D2), a riser pipe to give the required height (D3), and a
further elbow (D4), which is supported from the deck head by a exible hanger (D5), which supports the weight
of the system but permits movement side to side and fore and aft.
At this point water is injected into the exhaust through the injection elbow (D6), and the remainder of the
system follows usual wet exhaust practice, with a rubber hose falling to a transom tting.
The point of water injection should be at least 200mm (8”) above the water-line (D7), and the wet exhaust
should have an average fall of at least 10
o
. The table below shows the recommended minimum sizes.
Model Minimum diameter of dry part of
exhaust system
Minimum diameter of wet part of exhaust
system
415GM
40mm (1.6ins)
51mm (2ins)
422GM
63.5mm (2.5ins)422TGM
700GM
4GM
60mm (2.36ins) 76mm (3ins)
4TGM
4.4GM
4.4TGM
4.4TWGM
76mm (3ins)
102mm (4ins)4.4TW2GM
6TG2AM
6TWGM 127mm (5ins)
The dry part of the system
should be insulated to avoid
excessive heat loss to the engine
compartment.
Note: The bellows should be in an unstrained condition when installed, so that the full bellows movement is
available to absorb expansion and engine movement. The weight of the exhaust system should be supported
by brackets, and not carried by the bellows.